Williams-Crosby was born as Marceline Ann Williams on a ranch in North Hollywood, California. She began her career in show business as a singer and dancer before becoming a stunt performer. She is also a famous bodybuilder and a vegan. Williams-Crosby married Gregory Crosby – the first grandson of Bing Crosby and half-brother to Denise Crosby – on 26 August1989. They have one son, Luke.

In addition to her roles on Star Trek, she has appeared in or performed stunts for over 100 films and television programs, including Roseanne and From Dusk till Dawn, and has doubled for actresses like Louise Fletcher and Meg Foster.